Identifying the role of flagella in the transport of motile and nonmotile Salmonella enterica serovars

Influence of flagella and their property on the initial attachment behaviors of bacteria onto plastics

Flagella and their property would influence the initial attachment of bacteria onto plastics, yet their impacts have not been investigated. In present study, four types of E. coli with or without flagella as well as with normal or sticky flagella were utilized to investigate the effects of flagella and their property on the initial attachment behaviors of bacteria onto six types of plastics in freshwater systems. We found that E. coli with flagella exhibited better initial attachment performance onto all six types of plastics than strain without flagella. Flagella could help bacteria swim near to plastics, pierce the energy barrier, and subsequently attach onto plastics. With stronger adhesive force, sticky flagella could further facilitate bacterial attachment onto plastics. Moreover, flagella especially sticky flagella could help bacteria form more rigid attachment layer on plastics. Even with humic acid in suspensions or in river water, flagellar E. coli showed greater attachment onto plastics than E. coli without flagella. Humic acid might adsorb onto sticky flagella and thus decreased the attachment of bacteria with sticky flagella onto plastics. Obviously, flagella as well as their property would impact the initial attachment of bacteria onto plastics and the subsequent formation of plastisphere in freshwater.

Flagellar Phenotypes Impact on Bacterial Transport and Deposition Behavior in Porous Media: Case of Salmonella enterica Serovar Typhimurium

Bacterial contamination of groundwater has always been an ecological problem worthy of attention. In this study, Salmonella enterica serovar Typhimurium with different flagellar phenotypes mainly characterized during host-pathogen interaction were analyzed for their transport and deposition behavior in porous media. Column transport experiments and a modified mobile-immobile model were applicated on different strains with flagellar motility (wild-type) or without motility (ΔmotAB), without flagella (ΔflgKL), methylated and unmethylated flagellin (ΔfliB), and different flagella phases (fliC^ON, fljB^ON). Results showed that flagella motility could promote bacterial transport and deposition due to their biological advantages of moving and attaching to surfaces. We also found that the presence of non-motile flagella improved bacterial adhesion according to a higher retention rate of the ΔmotAB strain compared to the ΔflgKL strain. This indicated that bacteria flagella and motility both had promoting effects on bacterial deposition in sandy porous media. Flagella phases influenced the bacterial movement; the fliC^ON strain went faster through the column than the fljB^ON strain. Moreover, flagella methylation was found to favor bacterial transport and deposition. Overall, flagellar modifications affect Salmonella enterica serovar Typhimurium transport and deposition behavior in different ways in environmental conditions.

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

The global outbreak of coronavirus infectious disease-2019 (COVID-19) draws attentions in the transport and spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in aerosols, wastewater, surface water and solid wastes. As pathogens eventually enter the subsurface system, e.g., soils in the vadose zone and groundwater in the aquifers, they might survive for a prolonged period of time owing to the uniqueness of subsurface environment. In addition, pathogens can transport in groundwater and contaminate surrounding drinking water sources, possessing long-term and concealed risks to human society. This work critically reviews the influential factors of pathogen migration, unravelling the impacts of pathogenic characteristics, vadose zone physiochemical properties and hydrological variables on the migration of typical pathogens in subsurface system. An assessment algorithm and two rating/weighting schemes are proposed to evaluate the migration abilities and risks of pathogens in subsurface environment. As there is still no evidence about the presence and distribution of SARS-CoV-2 in the vadose zones and aquifers, this study also discusses the migration potential and behavior of SARS-CoV-2 viruses in subsurface environment, offering prospective clues and suggestions for its potential risks in drinking water and effective prevention and control from hydrogeological points of view.

Freeze-thaw cycles induce diverse bacteria release behaviors from quartz sand columns with different water saturations

Bacteria present in natural environment especially those in cold regions would experience freeze-thaw (FT) process during day-night and season turns. However, knowledge about the influence of FT on bacteria release behaviors in porous media was limited. In present study, the bacteria release behaviors from quartz sand columns without and with 1 and 3 FT treatment cycles under three water saturations (θ=100%, 90%, and 60%) were investigated. We found that for all three water saturated columns without FT treatment, negligible bacteria released from columns via background salt solution elution, while the subsequent release of bacteria from sand columns via low ionic strength (IS) solution elution decreased with decreasing column water saturations. More importantly, we found unlike the negligible bacteria release in columns without FT treatment, for columns with high saturations (θ=100% and 90%), FT treatment could promote bacteria release with background salt solution elution. Moreover, for high saturated columns, FT treatment would decrease subsequent bacteria release with low IS solution elution. This phenomenon was more obvious with increasing FT treatment cycles. In contrast, FT treatment had negligible influence on bacteria release from columns with lower saturation (θ=60%). The decreased bacterial sizes, the loss of bacterial flagella, as well as the change of local configuration of porous media (via changing water into ice and ice back into water) during the FT processes contributed to increased bacteria release via background salt solution elution from high saturated sand columns. While, the reduced amount of bacteria being retained at secondary energy minima drove to the subsequently decreased bacteria release via low IS solution elution. The results of this study clearly showed that for porous media with high saturations, FT cycles would increase the risk of bacteria detaching from porous media with flushing by the background solution.

Energy Taxis toward Redox-Active Surfaces Decreases the Transport of Electroactive Bacteria in Saturated Porous Media

The fate and transport of bacteria in porous media are essential for bioremediation and water quality control. However, the influence of biological activities like extracellular electron transfer (EET) and swimming motility toward granular media on cell transport remains unknown. Here, electroactive bacteria with higher Fe(III) reduction abilities were found to demonstrate greater retention in ferrihydrite-coated sand. Increasing the concentrations of the electron donor (1-10 mM lactate), shuttle (0-50 μM anthraquinone-2,6-disulfonate), and acceptor (ferrihydrite, MnO₂, or biochar) under flow conditions significantly reduced Shewanella oneidensis MR-1's mobility through redox-active porous media. The deficiency of EET ability or flagellar motion and inhibition of intracellular proton motive force, all of which are essential for energy taxis, enhanced MR-1's transport. It was proposed that EET could facilitate MR-1 to sense, tactically move toward, and attach on redox-active media surface, eventually improving its retention. Positive linear correlations were established among parameters describing MR-1's energy taxis ability (relative taxis index), cell transport behavior (dispersion coefficient and relative change of effluent percentage), and redox activity of media surface (reduction potential or electron-accepting rate), providing novel insights into the critical impacts of bacterial microscale motility on macroscale cell transport through porous media.

Flagella and Their Properties Affect the Transport and Deposition Behaviors of Escherichia coli in Quartz Sand

The effects of flagella and their properties on bacterial transport and deposition behaviors were examined by using four types of Escherichia coli (E. coli) with or without flagella, as well as with normal or sticky flagella. Packed column, quartz crystal microbalance with dissipation, visible parallel-plate flow chamber system, and visible flow chamber packed with porous media system were employed to investigate the deposition mechanisms of bacteria with different properties of flagella. We found that the presence of flagella favored E. coli deposition onto quartz sand/silica surfaces. Moreover, by changing the porous media porosity and directly observing the bacterial deposition process, local sites with high roughness, narrow flow channels, and grain-to-grain contacts were found to be the major sites for bacterial deposition. Particularly, flagella could help bacteria swim near and then deposit at these sites. In addition, we found that due to the stronger adhesive forces, sticky flagella could further enhance bacterial deposition onto quartz sand/silica surfaces. Elution experiments indicated that flagella could help bacteria attach onto sand surfaces more irreversibly. Clearly, flagella and their properties would have obvious impacts on the transport/deposition behaviors of bacteria in porous media.

Adhesion mediated transport of bacterial pathogens in saturated sands coated by phyllosilicates and Al-oxides

The current knowledge of bacterial migration is mainly derived from work using bare or Fe-coated quartz sands as porous media. However, mineral coatings on quartz by phyllosilicates and Al-oxides prevail in natural soils, and their effect on bacterial transport remains unknown. Herein, we systematically explored the transport of two bacterial pathogens (Escherichia coli and Staphylococcus aureus) through saturated bare quartz and those coated by kaolinite (KaoQuartz), montmorillonite (MontQuartz) or Al-oxides (AlQuartz) under various solution ionic strength (IS) and pH levels. Elevating IS or decreasing pH discouraged bacterial mobility in all cases, with one exception for the migration of S. aureus through AlQuartz at various IS levels. E. coli showed a higher mobility than S. aureus in all cases. All the three coatings, especially the Al-oxides inhibited bacterial transport through quartz. Overall, the two phyllosilicates-coated sands showed transport behaviors (mobility trends with IS, pH, and cell type) similar to those for the bare quartz which could be explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Nevertheless, for transport within AlQuartz, there were deviations between the observations and the DLVO predictions, probably because of the existence of non-DLVO forces such as hydrophobic and chemical interactions. More importantly, the bacterial retention was found to correlate well with the adhesion regardless of the solution condition and the bacteria and media type, thereby revealing a central role of adhesion in mediating migration through mineral-coated sands. These findings highlight the significance of mineral coating and adhesion in pathogen dissemination in natural soils.

Pyroelectric Effect Enables Simple and Rapid Evaluation of Biofilm Formation

Biofilms are detrimental to human life and industrial processes due to potential infections, contaminations, and deterioration. Therefore, the evaluation of microbial capability to form biofilms is of fundamental importance for assessing how different environmental factors may affect their vitality. Nowadays, the approaches used for biofilm evaluation are still poor in reliability and rapidity and often provide contradictory results. Here, we present what we call biofilm electrostatic test (BET) as a simple, rapid, and highly reproducible tool for evaluating in vitro the ability of bacteria to form biofilms through electrostatic interaction with a pyroelectrified carrier. The results show how the BET is able to produce viable biofilms with a density 6-fold higher than that on the control, after just 2 h incubation. The BET could pave the way to a rapid standardization of the evaluation of bacterial resistance among biofilm-producing microorganisms. In fact, due to its simplicity and cost-effectiveness, it is well suited for a rapid and easy implementation in a microbiology laboratory.

Influence of Bisphenol A on the transport and deposition behaviors of bacteria in quartz sand

The influence of Bisphenol A (BPA) on the transport and deposition behaviors of bacteria in quartz sand was examined in both NaCl (10 and 25 mM) and CaCl₂ solutions (1.2 and 5 mM) by comparing the breakthrough curves and retained profiles of cell with BPA in suspensions versus those without BPA. Gram-negative Escherichia coli and Gram-positive Bacillus subtilis were employed as model cells in the present study. The extended Derjaguin-Landau-Verwey-Overbeek interaction energy calculation revealed that the presence of BPA in cell suspensions led to a lower repulsive interaction between the cells and the quartz sand. This suggests that, theoretically, increased cell deposition on quartz sand would be expected in the presence of BPA. However, under all examined solution conditions, the presence of BPA in cell suspensions increased transport and decreased deposition of bacteria in porous media regardless of cell type, ionic strength, ion valence, the presence or absence of extracellular polymeric substances. We found that competition by BPA through hydrophobicity for deposition sites on the quartz sand surfaces was the sole contributor to the enhanced transport and decreased deposition of bacteria in the presence of BPA.

Effect of low-concentration rhamnolipid biosurfactant on Pseudomonas aeruginosa transport in natural porous media

The effect of low-concentrations of monorhamnolipid biosurfactant on transport of Pseudomonas aeruginosa ATCC 9027 in natural porous media (silica sand and a sandy soil) was studied with miscible-displacement experiments using artificial groundwater as the background solution. Transport of two types of cells was investigated, glucose- and hexadecane-grown cells with lower and higher cell surface hydrophobicity (CSH), respectively. The effect of hexadecane presence as a residual non-aqueous phase liquid (NAPLs) on transport was also examined. A clean-bed colloid deposition model was used to calculate deposition rate coefficients (k) for quantitative assessment. Significant cell retention was observed in the sand (81% and 82% for glucose- and hexadecane-grown cells, respectively). Addition of a low-concentration rhamnolipid solution enhanced cell transport, with 40 mg/L of rhamnolipid reducing retention to 50% and 60% for glucose- and hexadecane-grown cells, respectively. The k values for both glucose- and hexadecane-grown cells correlate linearly with rhamnolipid-dependent CSH represented as bacterial-adhesion-to-hydrocarbon rate of cells. Retention of cells by the soil was nearly complete (>99%). Addition of 40 mg/L rhamnolipid solution reduced retention to 95%. The presence of NAPLs in the sand increased the retention of hexadecane-grown cells with higher CSH. Transport of cells in the presence of the NAPL was enhanced by rhamnolipid at all concentrations tested, and the relative enhancement was greater than in was in the absence of NAPL. This study shows the importance of hydrophobic interaction on bacterial transport in natural porous media and the potential of using low-concentration rhamnolipid for facilitating the transport in subsurface for bioaugmentation efforts.

Influence of Perfluorooctanoic Acid on the Transport and Deposition Behaviors of Bacteria in Quartz Sand

The significance of perfluorooctanoic acid (PFOA) on the transport and deposition behaviors of bacteria (Gram-negative Escherichia coli and Gram-positive Bacillus subtilis) in quartz sand is examined in both NaCl and CaCl2 solutions at pH 5.6 by comparing both breakthrough curves and retained profiles with PFOA in solutions versus those without PFOA. All test conditions are found to be highly unfavorable for cell deposition regardless of the presence of PFOA; however, 7%-46% cell deposition is observed depending on the conditions. The cell deposition may be attributed to micro- or nanoscale roughness and/or to chemical heterogeneity of the sand surface. The results show that, under all examined conditions, PFOA in suspensions increases cell transport and decreases cell deposition in porous media regardless of cell type, presence or absence of extracellular polymeric substances, ionic strength, and ion valence. We find that the additional repulsion between bacteria and quartz sand caused by both acid-base interaction and steric repulsion as well as the competition for deposition sites on quartz sand surfaces by PFOA are responsible for the enhanced transport and decreased deposition of bacteria with PFOA in solutions.

Cotransport of bacteria with hematite in porous media: Effects of ion valence and humic acid

This study investigated the influence of multiple colloids (hematite and humic acid) on the transport and deposition of bacteria (Escherichia coli) in packed porous media in both NaCl (5 mM) and CaCl2 (1 mM) solutions at pH 6. Due to the alteration of cell physicochemical properties, the presence of hematite and humic acid in cell suspensions significantly affected bacterial transport and deposition in quartz sand. Specifically, the presence of hematite (5 mg/L) decreased cell transport (increased cell deposition) in quartz sand in both NaCl and CaCl2 solutions, which could be attributed to the less negative overall zeta potentials of bacteria induced by the adsorption of positively charged hematite onto cell surfaces. The presence of a low concentration (0.1 mg/L) of humic acid in bacteria and hematite mixed suspensions reduced the adsorption of hematite onto cell surfaces, leading to increased cell transport in quartz sand in NaCl solutions, whereas, in CaCl2 solutions, the presence of 0.1 mg/L humic acid increased the formation of hematite-cell aggregates and thus decreased cell transport in quartz sand. When the concentration of humic acid was increased to 1 mg/L, enhanced cell transport was observed in both NaCl and CaCl2 solutions. The decreased adsorption of hematite onto cell surfaces as well as the competition of deposition sites on quartz sand with bacteria by the suspended humic acid contributed to the increased cell transport.

Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in an ideal porous medium with hydrophilic or hydrophobic surfaces

The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low and high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k and rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R(2)=0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts.

Swimming Motility Reduces Deposition to Silica Surfaces

The transport and fate of bacteria in porous media is influenced by physicochemical and biological properties. This study investigated the effect of swimming motility on the attachment of cells to silica surfaces through comprehensive analysis of cell deposition in model porous media. Distinct motilities were quantified for different strains using global and cluster-based statistical analyses of microscopic images taken under no-flow condition. The wild-type, flagellated strain DJ showed strong swimming as a result of the actively swimming subpopulation whose average speed was 25.6 μm/s; the impaired swimming of strain DJ77 was attributed to the lower average speed of 17.4 μm/s in its actively swimming subpopulation; and both the nonflagellated JZ52 and chemically treated DJ cells were nonmotile. The approach and deposition of these bacterial cells were analyzed in porous media setups, including single-collector radial stagnation point flow cells (RSPF) and two-dimensional multiple-collector micromodels under well-defined hydrodynamic conditions. In RSPF experiments, both swimming and nonmotile cells moved with the flow when at a distance ≥20 μm above the collector surface. Closer to the surface, DJ cells showed both horizontal and vertical movement, limiting their contact with the surface, while chemically treated DJ cells moved with the flow to reach the surface. These results explain how wild-type swimming reduces attachment. In agreement, the deposition in micromodels was also lowest for DJ compared with those for DJ77 and JZ52. Wild-type swimming specifically reduced deposition on the upstream surfaces of the micromodel collectors. Conducted under environmentally relevant hydrodynamic conditions, the results suggest that swimming motility is an important characteristic for bacterial deposition and transport in the environment.

Modeling and analysis of hydrodynamic and physico-chemical effects in bacterial deposition on surfaces

The parallel-plate flow chamber (PFC) is often used for characterizing the propensity of microorganisms to attachment to surfaces. The model presented quantitatively analyzes the complex interplay of diffusion, convection, inertial lift, buoyancy, and surface forces in the PFC, which make it difficult to separate the surface- and microorganism-specific effects from the hydrodynamics. An empirical dimensionless factor K entering the boundary condition expresses enhancement of adhesion diffusion of microorganisms across a thin fluid layer adjacent to the surface by adhesion forces. The model examines the role of various factors (e.g., shear rate, size of bacterium, and strength of adhesion) on the rate of bacterial deposition. Using no adjustable parameter for strongly adhesive surfaces and K as the only adjustable parameter for repulsive or weakly adhesive surfaces, the model explains the observed decrease in deposition flux at high flow rates and compares reasonably with reported experimental results. The results suggest that the fitted value of K may be used for 'rating' the propensity of bacteria to deposit on surfaces and separating this from hydrodynamic effects.

Effects of outer membrane protein TolC on the transport of Escherichia coli within saturated quartz sands

The outer membrane protein (OMP) TolC is the cell surface component of several drug efflux pumps that are responsible for bacterial resistance against a variety of antibiotics. In this research, we investigated the effects of OMP TolC on E. coli transport within saturated sands through column experiments using a wild-type E. coli K12 strain (with OMP TolC), as well as the corresponding transposon mutant (tolC::kan) and the markerless deletion mutant (ΔtolC). Our results showed OMP TolC could significantly enhance the transport of E. coli when the ionic strength was 20 mM NaCl or higher. The deposition rate coefficients for the wild-type E. coli strain (with OMP TolC) was usually >50% lower than those of the tolC-negative mutants. The measurements of contact angles using three probe liquids suggested that TolC altered the surface tension components of E. coli cells and lead to lower Hamaker constants for the cell-water-sand system. The interaction energy calculations using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory suggested that the deposition of the E. coli cell primarily occurred at the secondary energy minimum. The depth of the secondary energy minimum increased with ionic strength, and was greater for the TolC-deletion strains under high ionic strength conditions. Overall, the transport behavior of three E. coli strains within saturated sands could be explained by the XDLVO calculations. Results from this research suggested that antibiotic resistant bacteria expressing OMP TolC could spread more widely within sandy aquifers.

Flagella-mediated differences in deposition dynamics for Azotobacter vinelandii in porous media

A multiscale approach was designed to study the effects of flagella on deposition dynamics of Azotobacter vinelandii in porous media, independent of motility. In a radial stagnation point flow cell (RSPF), the deposition rate of a flagellated strain with limited motility, DJ77, was higher than that of a nonflagellated (Fla(-)) strain on quartz. In contrast, Fla(-) strain deposition exceeded that of DJ77 in two-dimensional silicon microfluidic models (micromodels) and in columns packed with glass beads. Both micromodel and column experiments showed decreasing deposition over time, suggesting that approaching cells were blocked from deposition by previously deposited cells. Modeling results showed that blocking became effective for DJ77 strain at lower ionic strengths (1 mM and 10 mM), while for the Fla(-) strain, blocking was similar at all ionic strengths. In late stages of micromodel experiments, ripening effects were also observed, and these appeared earlier for the Fla(-) strain. In RSPF and column experiments, deposition of the flagellated strain was influenced by ionic strength, while ionic strength dependence was not observed for the Fla(-) strain. The observations in all three setups suggested flagella affect deposition dynamics and, in particular, result in greater sensitivity to ionic strength.